Thanks for playing and providing feedback. I'm glad you liked the concept.
I have to admit that there is both some design issues (played needing to use a lot of time just waiting and code problems (ghosts sometimes act weirdly) in the game. Some of the bugs I have managed to fix afterwards but unfortunately not all. Problems with jumping however should now be solved thanks to the help from Vendolis.
In level 4 (which I believe you are thinking about) the main puzzle is exactly what you had troubles with. In previous levels dying has been very easy so I tried to have this level have contrast to them by making getting to the spikes the most difficult part. It's trying to play with player expectations because so far the player has learned that everything is solved by using the ghosts. Getting to the spikes is possible to be done with only one character and as you said it is not even possible to get another character before you get to the spikes. The solution is to first move the middle platform down and then the left platform so there will be "stairs" going to the button on the left side. After getting there on needs to move the right platform and start building stairs again but this time towards the right side.
If you got to the level 4, you did not actually miss anything else than that level and the "narrative" ending level. I unfortunately did not have time to design more than 4 levels during the jam.